Adjustable precision spark gap



Jan. 11, 1966 o. JENSEN 3,229,145

ADJUSTABLE PRECISION SPARK GAP Filed Nov. 1, 1962 INVENTOR. Q 0770df/VSE/V United States Patent 3,229,145 ADJUSTABLE PRECISION SPARK GAPOtto Jensen, Malvern, Pa., assignor to I-T-E Circuit Breaker Company,Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 1, 1962,Ser. No. 234,770 1 Claim. (Cl. 313-146) This invention relates to anovel spark gap and more specifically relates to a novel adjustableprecision spark gap which is contained within a high dielectric medium.

Spark gaps are well known to the art and have use, for example, as afiring means to initiate the operation of protective electrical devicesin response to voltages which exceed some predetermined value. By way ofexample, spark gaps have extensive use in series capacitor protectorschemes of the type shown in copending application Serial No. 259,181filed February 18, 1963, in the name of Murray K. Price et al. entitledConstant Voltage Source for Operation of Series Capacitor BankProtective Equipment and assigned to the assignee of the presentinvention.

Where precise operation of the spark gap is required, it must bepossible to adjust the gap separation within very narrow limits. Thisproblem is complicated by random ionization in the gap area due tocosmic radiation which afiects the consistency of the gap ofcalibration.

In order to circumvent random ionization, a common practice has been topurposely increase the radiation level within the gap enclosure byintroducing a radioactive material and calibrating the gap at thisincreased ionization level. When this is done, random ionization due tocosmic radiation becomes a negligible influence on the gap calibration.

The present invention provides a novel precision spark gap in which thegap is enclosed in a high dielectric medium such as sulphur hexafluorideat atmospheric pressure or higher than atmospheric pressure, with anovel micrometer adjustment means entering the wall of the container ina sealed manner to permit adjustment of the gap separation.

The provision of the high dielectric gas medium permits operation of thegap in a very low ambient ionization environment with random ionizationdue to cosmic radiation being held to a minimum. Accordingly, the gapwhen initially calibrated, will hold its calibration with greataccuracy.

A micrometer adjustment is then introduced through a novel bellowswhereby the high dielectric gas remains sealed in the container whilestill permitting adjustment of the gap separation.

Accordingly, a primary object of this invention is to provide a highprecison spark gap.

Another object of this invention is to provide a novel spark gap whichoperates in a low ionization environment.

A further object of this invention is to provide a novel adjustableprecision spark gap.

Another object of this invention is to provide a spark gap enclosed in ahigh dielectric gas where the gap separation is adjustable by meansexternal of the spark gap housing.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings, inwhich:

FIGURE 1 shows a side cross-sectional view of a spark gap constructed inaccordance with the present invention.

FIGURE 2 is a top plan view of the front portion of teh spark gap toillustrate the micrometer adjustment means.

3,229,145 Patented Jan. 11, 1966 "ice Referring now to FIGURE 1, thespark gap container is formed of a hollow porcelain insulator 10 whichmay be tubular which is sealed at either end by insulation caps 11 and12 which are of any appropriate dielectric medium. Gaskets 11a and 1211are secured between caps 11 and 12 respectively and insulator 10.

Cap 11 is secured to insulator 10 by means of bolts such as bolts 13 and14 which pass through appropriate openings in cap 11 and threadablyreceive a clamping ring 15 which is drawn into engagement with shoulder16 in insulator 10. The clamping ring 15 is secured in place by anappropriate nut and washer arrangement such as nuts 17 and 18 andwashers 19 and 20 respectively.

A similar clamping arrangement is provided for securing end cap 12 toinsulator 10 which includes clamping ring 21 which is bolted againstshoulder 22 in the insulator 10.

Cap 12 is formed with an inwardly extending section 23 which has anopening therethrough for receiving threaded bolt 24. The left-hand endof bolt 24 is threaded into a threaded opening in electrode 25 with anappropriate sealing ring 26 forming a gas tight connection betweenelectrode 25 and section 23. The right-hand end of bolt 24 receives thetwo nuts 27 and 28 which are secured against the right-hand surface ofcap 12 to hold electrode 25 in position.

End cap 11 has extending section 30 which has an opening therethroughfor receiving the threaded bolt 31. The threaded bolt 31' has a keyway32 therein which receives key 33 carried by extension 30 whereby bolt 31is movable along the axis of member 30 but it cannot be rotated.

The right-end end of bolt 31 is threadably receivedby insulation cap 40and electrode 41 where a sealing gasket 42 forms a seal between theopposing surfaces of cap 40 and electrode 41. A biasing spring 42 isthen captured between the right-hand surface of cap 11 and the left-handsurface of cap 40 to bias electrode 41, cap 40 and. bolt 31 towardelectrode 25.

In order to control the motion of electrode 41 to the right, the bolt 31fits through a micrometer adjustment head 50 which is threaded onto bolt31. A retaining nut 51 which is tightened after the micrometer head 50has been set holds the bolt 31 in its adjusted position. The micrometerhead 50 is calibrated with indicia 52, as best seen in FIGURE 2, whichis rotatable with respect to a pointer 53 which is secured to cap 11 byscrews 54 and 55.

A bellows 60 is then secured between caps 11 and 40 in any desiredmanner as by cementing so that the inner chamber 61 which contains theouter surfaces of electrodes 25 and 41 is isolated from areas internalof bellows 60.

Each of caps 11 and 12 then have tapered plugs and 71 which may beremoved to permit the introduction of a high dielectric gas such assulphur hexafluoride into chamber 61 to completely fill chamber 61 withthis gas at atmospheric pressure or higher.

Appropriate securing means can secure plugs 70 and 71 with respect tocaps 11 and 12 respectively after the filling operation has beencompleted.

In operation, the bolts 24 and 31 which are of conductive material serveas the terminals of the spark gap device, where the active gapelectrodes are formed by electrodes 25 and 41 which are of anappropriate material for the purpose.

In order to adjust the spacing between electrodes 25 and 41, the nut 51is loosened and micrometer head 50 is rotated. The rotation ofmicrometer head on threaded bolt 31 will cause bolt 31 to move axiallywhereby the axial position of electrode 41 changes with respect to thestationary electrode 25.

This motion is permitted by bellows 60 and is in opposition tocompression spring 42 which has a fully extended length considerably inexcess of the maximum travel of electrode 41. Once the calibratedposition is achieved, nut 51 is tightened.

It is to be particularly noted that this adjustment may be carried outeven though the chamber 61 is filled with gas. That is to say, thebellows arrangement 412 permits transmission of. adjusting motionthrough cap 11 while retaining the chamber 61 in a sealed condition.

Although this invention has been described with respect to preferredembodiments thereof, it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of this invention be limited not byspecific disclosure herein but only by the appended claim.

- What is claimed is: I

A precision spark gap comprising a sealed chamber, a first electrodesecured to a first wall of said chamber, and a second electrode securedto a second wall of said chamber; said chamber being filled with a highdielectric gas at approximately atmospheric pressure; said secondelectrode being secured to said chamber by an adjustable member; saidadjustable member passing through an opening in said chamber and beingaxially movable through said opening in said chamber; the portion ofsaid adjustable member extending into said chamber being secured to oneend of a closed bellows; the other end of said bellows being secured tosaid chamber and enclosing said opening; said second electrode beingexternal of the interior of said bellows whereby said adjustable memberis operable from regions external of said sealed chamber and said sealedchamber is sealed from said opening by said bellows; said sealed chambercomprising a hollow tubular insulator enclosed at either end byrespective first'and second end caps of insulation material; said firstand second electrodes being secured to said first and second end capsrespectively; said first and second end caps having central sectionsprojecting inwardly of said tubular insulator; said first and secondelectrodes being "carried at the ends of said first and second inwardlyprojecting sections respectively; said adjustable member extendingthrough said inwardly projecting section of said second end cap;terminals for said first and second electrodes extending through saidfirst and second inwardly projecting sections; said terminal for saidfirst electrode comprising a threaded bolt for securing said firstelectrode to said end of said first inwardly projecting section of saidfirst end cap; said terminal for said second electrode comprising saidadjustable member; said adjustable member having a threaded end forthreadably receiving said second electrode; andmicrometer adjustmentmeans threadably secured to the end of said adjustable member extendingout of said sealed chamber; the interior of said bellows receiving acompression spring to bias the ends of said bellows away from oneanother.

References Cited by the Examiner OTHER REFERENCES Pub., Lingal, H. 1.,and Owens, J. B.: A New High Voltage Outdoor Load Interrupter Switch. InA.I.E.E. Transactions, 1953, Vol. 72, Part III; pages 293-295.

GEORGE N. WESTBY, Primary Examiner.

